The process of subjecting material in liquid form to a heat treatment has been carried out in various fields where liquid products are being prepared for use, and various methods and apparatus have been developed for attaining the desired degree of heating. In common with the equipment of the present invention, some apparatus involves directing the liquid through a heated chamber in film form to heat it. The patent to Evans, U.S. Pat. No. 3,032,423, discloses apparatus for directing liquid in planar sheet-like form downwardly from inlet tubes through the interior of a heated vessel. Similarly, the patent to Davies, U.S. Pat. No. 3,771,434, disclosed apparatus for directing sheet-like films of liquid through a heat-treatment chamber. The patent to Davies, U.S. Pat. No. 3,847,714, teaches the use of a plurality of nozzles spaced in a circular path and arranged to direct liquid downwardly to form a descending curtain of liquid. Zlokarnik et al, U.S. Pat. No. 4,162,971, discloses a generally conical deflector that is disposed in the flow path of incoming liquid and is arranged to deflect the liquid outwardly and distribute it across the full cross-section of a mixing chamber. None of these patents teach or suggest the concept of forming the liquid into a descending, continuous curtain wherein the diameter of the curtain continually increases as the film moves downwardly and outwardly, and the thickness of the film decreases progressively.
An object of the invention is therefore to provide a method for heat treating liquid food products in such a way that the surface area of the film increases rapidly, thus exposing new surfaces to the heating medium, while the thickness of the film decreases in thickness to cause an increase in the rate of heat absorption by the liquid thereby providing a relatively short time-temperature ratio.
Another object is to provide apparatus in which a liquid, such as milk, can be raised to a sterilizing temperature in an atmosphere of steam before the milk contacts a surface that is much hotter than itself, thus preventing burning-on or off-flavor of the milk.